In a storage system according to a conventional technology, data written from a host computer is written into a cache memory before being written onto a disk drive. The moment that the data is written into the cache memory, the storage system notifies the host computer that a write process has been completed, which improves responsiveness to the host computer.
A DRAM is generally used as the cache memory in terms of the number of times that a read/write is performed and an access speed. Therefore, the data stored in the cache memory volatilizes (disappears) when power to the storage system is shut down, which necessitates backup of data (dirty data) before being written onto the disk drive by supplying power from a battery in case of service interruption.
Further, JP 2004-21811 A discloses a storage system in which a non-volatile memory is used as a cache memory to thereby prevent data from volatilizing (disappearing) even when power is shut down.